Harry Maguire had a last-gasp header superbly turned on to a post by Baggies goalkeeper Sam Johnstone.
Having won all of its previous seven away league matches in which United conceded first, Solskjaer will be frustrated by his side’s poor response in this costly draw at the Hawthorns.
Diagne scored his first goal for the club, his hand in Victor Lindelof’s face overlooked, but Fernandes levelled superbly at the end of the first half. He fired home a stunning leveler in the 44th minute, meeting Luke Shaw’s cross with a fine hooked effort that flew into the top left-hand corner.
The second half was more open and eventful.
Referee Craig Pawson overturned his decision to award a penalty for Semi Ajayi’s foul on Maguire after reviewing footage on the monitor, but offside would have come into play anyway if he had stuck with his decision.
Johnstone denied Mason Greenwood before Darnell Furlong cleared Scott McTominay’s effort off the line, while at the other end David De Gea prevented Diagne securing a shock win with a superb double save.
Diagne only had himself to blame in the 78th minute as he somehow failed to score. Having shaken off Maguire to go through one-on-one with De Gea, the ball looped up after his initial shot was saved and Diagne looked set to nod into an empty net until the goalkeeper got back superbly to claw away.
Wolves come back to beat Southampton
At Southampton, Wanderers came from behind to beat Southampton 2-1, inflicting their sixth league defeat in a row.
Danny Ings gave the home side the lead but a Ruben Neves penalty and a superb Pedro Neto goal gave Wolves all three points.
Southampton have won only once in their last 11 league matches and Hasenhuettl was at a loss to explain a result, which condemned his club to a sixth consecutive league loss for the first time in their history.
“We know what happened today – it’s hard to explain this defeat,” Hasenhuettl told Amazon Prime. “Until their penalty they had no chances at goal.”
Southampton took the lead when Stuart Armstrong burst down the flank and left two defenders for dead before delivering a cross to pick out Ings who emphatically volleyed home.
But Wolves were more fluid going forward in the second half and were handed a lifeline when Nelson Semedo’s cross hit Ryan Bertrand’s arm. Neves made no mistake in beating Alex McCarthy from the penalty spot.
Neto sealed the win with a solo goal in the 66th minute, side-stepping Jannik Vestergaard before striking the ball past McCarthy from an acute angle.
“It was a very tough game, both halves were very tough,” Wolves manager Nuno Espirito Santo said. “In the first half Southampton managed the game. In the second half we were on the front foot, scored two goals and then defended very well.”